Those apps aren't actually running. It's not doing anything to your battery.
The apps save the state they were in prior to closing and open back up to the same place when you click them.
Only some apps actually run, but what they can do is very limited. This is how multitasking on the phone should be.
Only apps that record, play music or do other stuff that must continue when exited actually keep running.
If you want to close the apps in question just to feel better, just press and hold until they shake then press the close icon.
I assure you though, they are not draining your battery.
Things that do drain battery: having screen above 50% brightness, opening apps constantly, long cellular usage (phone calls and data over 3G).
To conserve battery, I keep my screen at 50%, don't download apps all the time, and connect to wifi whenever possible.
Wifi saves battery because the phone doesn't have to constantly connect to a cell tower.
Also, get over the idea that the battery needs to stay above 50% by the end of the day. (I had this problem at first)